A. Field of the Invention
The present invention relates to tools and implements for making elongated circular cross-section bore holes such as post holes into soil beneath the surface of the ground. More particularly, the invention relates to a hole digger tool and apparatus which uses a vacuum pump to remove soils severed by cutting teeth and has a rotating unclogger bar to break up mud or clay clogs which could impede removal of dislodged soil.
B. Description of Background Art
There are a variety of situations which require making elongated, relatively deep holes into the ground. These include digging generally cylindrically-shaped holes for receiving fence posts, sign posts and the like. Such holes have a typical diameter range of from about 4 inches to about 12 inches, and a depth of 3 to 6 feet or more.
Digging relatively deep, elongated holes such as post holes in the ground tends to be a tedious, slow, labor intensive task, when using conventional manually operated, manually powered digging implements. A widely used manually powered, “clam-shell” post hole digger includes a pair of shovels, each of which has a generally semi-circularly curved blade. The shovel blades are fixed to the lower ends of upwardly protruding handles which are pivotably mounted to one another at a location between the shovel blades and the upper ends of the handles, and arranged so that the concave surfaces of the shovel blades confront one another to define therebetween a generally cylindrically-shaped space corresponding to a hole to be dug.
Clam-shell post hole diggers are used by pivoting the upper ends of the handles also orienting the shovel blades at the lower ends of the handles in generally parallel alignment. The handles are then grasped by an operator to orient them vertically, i.e., perpendicularly to a ground surface into which a post hole is to be dug. The operator then brings his arms down forcefully towards the surface of the ground, thus causing pointed tips of the shovel blades to penetrate the ground soil, and the handles are rocked back and forth in a horizontal direction, to thus impart a twisting cutting motion to the shovel blades.
Next, the upper ends of the handles are drawn apart to thus pivot the shovel blades towards one another, underneath soil which has been loosened by downward and twisting cutting actions of the shovel blades. The claim-shell digger tool is then raised above the ground to thus withdraw the shovel blades from the ground and thereby remove the severed soil, which may then be dumped at any convenient location. This is done by pushing the upper ends of the handles together, thus causing the inner facing concave surfaces of the shovel blades to pivot away from one another, allowing soil supported on those surfaces to fall away from the blades.
The handles are once again put into parallel alignment, and claim-shell digger tool is again thrust downward to thus drive the shovel blades downward into the hole being dug to thereby begin a new cycle of soil excavating. These cycles are repeated as often as required to dig a hole of a desired depth. As can be well appreciated, digging post holes with a clam-shell digging tool of this type is a very laborious, slow task.
Another method of forming post holes which is in common use employs a large diameter auger that is rotated by an electric, hydraulic or air-driven motor. Boring post holes with a powered auger of this type is much quicker and easier than using a claim-shell type digger tool, but the cost of such devices, and the requirement of providing electric, hydraulic or compressed air power to them, limits the extent of their use.
In apparent recognition of certain limitations of clam-shell or auger-type post hole diggers, U.S. Pat. No. 7,185,720 disclosed a hole digger which includes an elongated, skeletonized cylinder that has circumferentially spaced apart, elongated bars which are fastened at the upper ends thereof to the periphery of an upper mounting ring, and near the lower ends of the bars to a lower, mounting ring. The bars extend below the lower mounting ring and terminate in wedge-shaped, pointed cutting teeth.
The digging tool disclosed in U.S. Pat. No. 7,185,720 includes a straight, hollow vacuum tube which fits coaxially down through the bore of the skeletonized frame and is longitudinally movable therewithin. The upper end of the vacuum tube is connected through a flexible vacuum hose to a vacuum source, such as a wet-or-dry shop vacuum unit. The tool is used by pressing the pointed edges of the cutting teeth into a soil surface, twisting the unit back and forth with respect to its longitudinal axis to thus cause the teeth to exert a rotary cutting action on the soil surface, and oscillating the vacuum tube up and down to thus vacuum up severed soil.
While the hole digger implement disclosed in U.S. Pat. No. 7,185,720 appears to be an improvement over certain prior art hole diggers such as clam-shell type hole diggers, the present inventor has found that diggers of the type disclosed in the '720 patent have certain limitations. For example, the requirement that the vacuum tube in the '720 digger be oscillated up and down can become burdensome. Also, the present inventor has found that using vacuum assisted hole diggers of the type described in U.S. Pat. No. 7,185,720 in wet, muddy or clay soil can be problematic, because the mud or clay tends to lodge within the vacuum tube, thus clogging the bore of the vacuum tube and preventing soil from being drawn upwardly through the tube.
The foregoing considerations in part prompted the present invention, which is described in detail below.